Organic electroluminescent device comprising an electron buffer layer and an electron transport layer

ABSTRACT

The present disclosure relates to an organic electroluminescent device. The organic electroluminescent device of the present disclosure comprises a specific combination of an electron buffer material and an electron transport material which can provide high efficiency and/or long lifespan.

TECHNICAL FIELD

The present disclosure relates to an organic electroluminescent devicecomprising an electron buffer layer and an electron transport layer.

BACKGROUND ART

An electroluminescent (EL) device is a self-light-emitting device withthe advantages of providing a wider viewing angle, a greater contrastratio, and a faster response time. The first organic EL device wasdeveloped by Eastman Kodak, by using small aromatic diamine moleculesand aluminum complexes as materials for forming a light-emitting layer(see Appl. Phys. Lett. 51, 913, 1987).

An organic EL device changes electric energy into light by the injectionof a charge into an organic light-emitting material, and commonlycomprises an anode, a cathode, and an organic layer formed between thetwo electrodes. The organic layer of the organic EL device may becomposed of a hole injection layer, a hole transport layer, an electronblocking layer, a light-emitting layer (containing host and dopantmaterials), an electron buffer layer, a hole blocking layer, an electrontransport layer, an electron injection layer, etc.; the materials usedin the organic layer can be classified into a hole injection material, ahole transport material, an electron blocking material, a light-emittingmaterial, an electron buffer material, a hole blocking material, anelectron transport material, an electron injection material, etc.,depending on functions. In the organic EL device, holes from an anodeand electrons from a cathode are injected into a light-emitting layer byelectric voltage, and an exciton having high energy is produced by therecombination of the holes and electrons. The organic light-emittingcompound moves into an excited state by the energy and emits light fromenergy when the organic light-emitting compound returns to the groundstate from the excited state.

In an organic EL device, an electron transport material activelytransports electrons from a cathode to a light-emitting layer andinhibits transport of holes which are not recombined in thelight-emitting layer to increase recombination opportunity of holes andelectrons in the light-emitting layer. Thus, electron-affinitivematerials are used as an electron transport material. Organic metalcomplexes having light-emitting function such as Alq₃ are excellent intransporting electrons, and thus have been conventionally used as anelectron transport material. However, Alq₃ has problems in that it movesto other layers and shows reduction of color purity when used in bluelight-emitting devices. Therefore, new electron transport materials havebeen required, which do not have the above problems, are highlyelectron-affinitive, and quickly transport electrons in organic ELdevices to provide organic EL devices having high luminous efficiency.

Further, the electron buffer layer is a layer for solving the problem ofa change in luminance caused by the change of a current characteristicof the device when exposed to a high temperature during a process ofproducing a panel. In order to obtain a similar current characteristicand a stability to high temperature compared to a device without anelectron buffer layer, the characteristic of the compound comprised inthe electron buffer layer is important.

In addition, a fluorescent material provides lower efficiencies than aphosphorescent material. Accordingly, there have been attempts toimprove efficiencies by developing a specific fluorescent material suchas a combination of an anthracene-based host and a pyrene-based dopant.However, the proposed combination makes holes become greatly trapped,which can cause light-emitting sites in a light-emitting layer to shiftto the side close to a hole transport layer, thereby light being emittedat an interface. The light emission at the interface decreases lifespanof a device, and efficiencies are not satisfactory. Accordingly, therehave been attempts to solve both efficiency and lifespan problems byinserting an electron buffer layer between the light-emitting layer andthe electron transport layer as a method to solve the problems offluorescent materials.

Korean Patent Appln. Laying-Open No. 2015-0080213 A discloses an organicelectroluminescent device comprising a bilayer-structured electrontransport layer comprising an anthracene-based compound and aheteroaryl-based compound.

Korean Patent Appln. Laying-Open No. 2016-0034804 A discloses an organicelectroluminescent device comprising a compound in which anitrogen-containing heteroaryl is bonded to a benzocarbazole, etc., viaa linker comprising two or more aryl groups as an electron transportmaterial.

Korean Patent Appln. Laying-Open No. 2015-0108330 A discloses an organicelectroluminescent device comprising a compound in which anitrogen-containing heteroaryl is bonded to a carbazole, etc., as anelectron buffer material.

However, the above references fail to specifically disclose an organicelectroluminescent device comprising a compound comprising anitrogen-containing heteroaryl as an electron buffer material and acompound in which a nitrogen-containing heteroaryl is bonded to abenzocarbazole, etc., via a linker of a naphthylene as an electrontransport material. In addition, when using a hetero compound in which anitrogen-containing heteroaryl is bonded to a benzocarbazole, etc., viaa linker comprising two or more aryl groups as an electron transportmaterial, the LUMO energy level gets lower. Thus, it is not appropriateas an electron transport material.

DISCLOSURE OF THE INVENTION Problems to be Solved

The objective of the present disclosure is to provide an organicelectroluminescent device having high efficiency and/or long lifespan bycomprising a specific combination of an electron buffer material and anelectron transport material.

Solution to Problems

The present inventors found that the above objective can be achieved byan organic electroluminescent device comprising a first electrode, asecond electrode facing the first electrode, a light-emitting layerbetween the first electrode and the second electrode, and an electrontransport layer and an electron buffer layer between the light-emittinglayer and the second electrode, wherein the electron buffer layercomprises a compound represented by the following formula 1, and theelectron transport layer comprises a compound represented by thefollowing formula 2:

wherein

X₁ to X₅ each independently represent CR₁ or N;

R₁ represents hydrogen, a substituted or unsubstituted (C1-C30)alkyl, asubstituted or unsubstituted (C3-C30)cycloalkyl, a substituted orunsubstituted (C6-C30)aryl, a substituted or unsubstituted (5- to30-membered)heteroaryl, a substituted or unsubstitutedtri(C1-C30)alkylsilyl, a substituted or unsubstitutedtri(C6-C30)arylsilyl, a substituted or unsubstituteddi(C1-C30)alkyl(C6-C30)arylsilyl, a substituted or unsubstituted(C1-C30)alkyldi(C6-C30)arylsilyl, a substituted or unsubstituted mono-or di-(C1-C30)alkylamino, or a substituted or unsubstituted mono- ordi-(C6-C30)arylamino; or may be linked to an adjacent substituent toform a substituted or unsubstituted, mono- or polycyclic, (C3-C30)alicyclic, aromatic, or a combination of alicyclic and aromatic ring,whose carbon atom(s) may be replaced with at least one heteroatomselected from nitrogen, oxygen, and sulfur;

L represents a single bond, a substituted or unsubstituted(C6-C50)arylene, or a substituted or unsubstituted (5- to50-membered)heteroarylene;

Ar represents a substituted or unsubstituted (C6-C50)aryl, or asubstituted or unsubstituted (5- to 50-membered)heteroaryl;

Ar₁ and Ar₂ each independently represent a substituted or unsubstituted(C6-C30)aryl;

L₁ represents a naphthylene;

ring A and ring B each independently represent a benzene, aphenylbenzene, or a naphthalene, with a proviso that at least one ofring A and ring B represent naphthalene;

n represents an integer of 1 to 3; and

the heteroaryl(ene) contains at least one heteroatom selected from B, N,O, S, Si, and P.

Effects of the Invention

The present disclosure provides an organic electroluminescent devicehaving high efficiency and/or long lifespan, and a display system or alighting system can be produced by using the device.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a schematic sectional view of an organicelectroluminescent device according to one embodiment of the presentdisclosure.

FIG. 2 illustrates an energy gap relationship among the layers of theorganic electroluminescent device according to one embodiment of thepresent disclosure.

FIG. 3 is a graph illustrating a current efficiency versus a luminanceof organic electroluminescent devices of Comparative Example 1 andDevice Example 2.

EMBODIMENTS OF THE INVENTION

Hereinafter, the present disclosure will be described in detail.However, the following description is intended to explain the invention,and is not meant in any way to restrict the scope of the invention.

The term “organic electroluminescent compound” in the present disclosuremeans a compound that may be used in an organic electroluminescentdevice, and may be comprised in any layer constituting an organicelectroluminescent device, as necessary.

The term “organic electroluminescent material” in the present disclosuremeans a material that may be used in an organic electroluminescentdevice, and may comprise at least one compound. The organicelectroluminescent material may be comprised in any layer constitutingan organic electroluminescent device, as necessary. For example, theorganic electroluminescent material may be a hole injection material, ahole transport material, a hole auxiliary material, a light-emittingauxiliary material, an electron blocking material, a light-emittingmaterial, an electron buffer material, a hole blocking material, anelectron transport material, or an electron injection material.

In an organic electroluminescent device comprising first and secondelectrodes, and a light-emitting layer, an electron buffer layer can beinserted between the light-emitting layer and the second electrode tofocus on obtaining high efficiency and/or long lifespan due to electroninjection controlled by the LUMO energy level of the electron bufferlayer.

Originally, LUMO (lowest unoccupied molecular orbital) energy and HOMO(highest occupied molecular orbital) energy levels have negative values.However, for convenience, LUMO energy level (A) and HOMO energy levelare expressed in absolute values in the present disclosure. In addition,the values of the LUMO energy level are compared based on absolutevalues. Values measured by density functional theory (DFT) are used forLUMO energy levels and HOMO energy levels in the present disclosure.

The LUMO energy levels can be easily measured by known various methods.Generally, LUMO energy levels are measured by cyclic voltammetry orultraviolet photoelectron spectroscopy (UPS). Therefore, a personskilled in the art can easily comprehend the electron buffer layer,light-emitting layer, and electron transport layer that satisfy theequational relationship of the LUMO energy levels of the presentdisclosure, and practice the present disclosure. HOMO energy levels canbe easily measured by the same method of measuring LUMO energy levels.

The present disclosure is directed to an organic electroluminescentdevice comprising a first electrode, a second electrode facing the firstelectrode, a light-emitting layer between the first electrode and thesecond electrode, and an electron transport layer and an electron bufferlayer between the light-emitting layer and the second electrode, whereinthe electron buffer layer comprises a compound represented by formula 1,and the electron transport layer comprises a compound represented byformula 2.

The electron buffer layer and the electron transport zone are insertedbetween the light-emitting layer and the second electrode. The electronbuffer layer may be located between the light-emitting layer and theelectron transport zone, or between the electron transport zone and thesecond electrode.

The electron buffer material comprised in the electron buffer layerindicates a material controlling an electron flow. Therefore, theelectron buffer material may be, for example, a material which trapselectrons, blocks electrons, or lowers an energy barrier between anelectron transport zone and a light-emitting layer. In the organicelectroluminescent device, the electron buffer material may be used forpreparing an electron buffer layer, or may be incorporated into anotherarea such as an electron transport zone or a light-emitting layer. Theelectron buffer layer may be formed between a light-emitting layer andan electron transport zone, or between an electron transport zone and asecond electrode of an organic electroluminescent device. The electronbuffer material may further comprise materials which are conventionallyused for preparing an organic electroluminescent device besides thecompound of formula 1.

The electron transport material comprised in the electron transportlayer actively transports electrons from a cathode to a light-emittinglayer and inhibits transport of holes which are not recombined in thelight-emitting layer to increase recombination opportunity of holes andelectrons in the light-emitting layer. Thus, electron-affinitivematerials are used as an electron transport material. The electrontransport layer may be formed in an electron transport zone between asecond electrode and a light-emitting layer of an organicelectroluminescent device. The electron transport material may furthercomprise materials which are conventionally used for preparing anorganic electroluminescent device besides the compound of formula 2.

Herein, “(C1-C30)alkyl” is meant to be a linear or branched alkyl having1 to 30 carbon atoms constituting the chain, in which the number ofcarbon atoms is preferably 1 to 10, more preferably 1 to 6, and includesmethyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, etc.“(C2-C30)alkenyl” is meant to be a linear or branched alkenyl having 2to 30 carbon atoms constituting the chain, in which the number of carbonatoms is preferably 2 to 20, more preferably 2 to 10, and includesvinyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 3-butenyl,2-methylbut-2-enyl, etc. “(C2-C30)alkynyl” is a linear or branchedalkynyl having 2 to 30 carbon atoms constituting the chain, in which thenumber of carbon atoms is preferably 2 to 20, more preferably 2 to 10,and includes ethynyl, 1-propynyl, 2-propynyl, 1-butynyl, 2-butynyl,3-butynyl, 1-methylpent-2-ynyl, etc. “(C3-C30)cycloalkyl” is a mono- orpolycyclic hydrocarbon having 3 to 30 ring backbone carbon atoms, inwhich the number of carbon atoms is preferably 3 to 20, more preferably3 to 7, and includes cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl,etc. “(3- to 7-membered)heterocycloalkyl” is a cycloalkyl having atleast one heteroatom selected from the group consisting of B, N, O, S,Si, and P, preferably O, S, and N, and 3 to 7 ring backbone atoms, andincludes tetrahydrofuran, pyrrolidine, thiolan, tetrahydropyran, etc.“(C6-C30)aryl(ene)” is a monocyclic or fused ring derived from anaromatic hydrocarbon having 6 to 30 ring backbone carbon atoms and maybe partially saturated, in which the number of ring backbone carbonatoms is preferably 6 to 20, more preferably 6 to 15, and includesphenyl, biphenyl, terphenyl, naphthyl, binaphthyl, phenylnaphthyl,naphthylphenyl, fluorenyl, phenylfluorenyl, benzofluorenyl,dibenzofluorenyl, phenanthrenyl, phenylphenanthrenyl, anthracenyl,indenyl, triphenylenyl, pyrenyl, tetracenyl, perylenyl, chrysenyl,naphthacenyl, fluoranthenyl, etc. “(3- to 30-membered)heteroaryl(ene)”is an aryl group having at least one, preferably 1 to 4 heteroatomsselected from the group consisting of B, N, O, S, Si, and P, and 3 to 30ring backbone atoms, in which the number of ring backbone atoms ispreferably 3 to 20, more preferably 5 to 15; is a monocyclic ring, or afused ring condensed with at least one benzene ring; may be partiallysaturated; may be one formed by linking at least one heteroaryl or arylgroup to a heteroaryl group via a single bond(s); and includes amonocyclic ring-type heteroaryl including furyl, thiophenyl, pyrrolyl,imidazolyl, pyrazolyl, thiazolyl, thiadiazolyl, isothiazolyl,isoxazolyl, oxazolyl, oxadiazolyl, triazinyl, tetrazinyl, triazolyl,tetrazolyl, furazanyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl,etc., and a fused ring-type heteroaryl including benzofuranyl,benzothiophenyl, isobenzofuranyl, dibenzofuranyl, dibenzothiophenyl,benzonaphthothiophenyl, benzimidazolyl, benzothiazolyl,benzoisothiazolyl, benzoisoxazolyl, benzoxazolyl, isoindolyl, indolyl,indazolyl, benzothiadiazolyl, quinolyl, isoquinolyl, cinnolinyl,quinazolinyl, quinoxalinyl, carbazolyl, phenoxazinyl, phenanthridinyl,benzodioxolyl, etc. “Halogen” includes F, Cl, Br, and I.

Herein, “substituted” in the expression “substituted or unsubstituted”means that a hydrogen atom in a certain functional group is replacedwith another atom or functional group, i.e., a substituent. Thesubstituents of the substituted alkyl, the substituted cycloalkyl, thesubstituted aryl(ene), the substituted heteroaryl(ene), the substitutedtrialkylsilyl, the substituted triarylsilyl, the substituteddialkylarylsilyl, the substituted alkyldiarylsilyl, the substitutedmono- or di-alkylamino, the substituted mono- or di-arylamino, and thesubstituted mono- or polycyclic, alicyclic, aromatic, or a combinationof alicyclic and aromatic ring in R₁, L, Ar, Ar₁, and Ar₂ in formulae 1and 2 each independently are at least one selected from the groupconsisting of deuterium, a halogen, a cyano, a carboxyl, a nitro, ahydroxyl, a (C1-C30)alkyl, a halo(C1-C30)alkyl, a (C2-C30)alkenyl, a(C2-C30)alkynyl, a (C1-C30)alkoxy, a (C1-C30)alkylthio, a(C3-C30)cycloalkyl, a (C3-C30)cycloalkenyl, a (3- to7-membered)heterocycloalkyl, a (C6-C30)aryloxy, a (C6-C30)arylthio, a(3- to 30-membered)heteroaryl unsubstituted or substituted with a(C6-C30)aryl, a (C6-C30)aryl unsubstituted or substituted with a (3- to30-membered)heteroaryl, a tri(C1-C30)alkylsilyl, a tri(C6-C30)arylsilyl,a di(C1-C30)alkyl(C6-C30)arylsilyl, a (C1-C30)alkyldi(C6-C30)arylsilyl,an amino, a mono- or di-(C1-C30)alkylamino, a mono- ordi-(C6-C30)arylamino, a (C1-C30)alkyl(C6-C30)arylamino, a(C1-C30)alkylcarbonyl, a (C1-C30)alkoxycarbonyl, a (C6-C30)arylcarbonyl,a di(C6-C30)arylboronyl, a di(C1-C30)alkylboronyl, a(C1-C30)alkyl(C6-C30)arylboronyl, a (C6-C30)aryl(C1-C30)alkyl, and a(C1-C30)alkyl(C6-C30)aryl.

According to one embodiment of the present disclosure, the compound offormula 1 comprised in the electron buffer layer may be represented bythe following formula 3 or 4:

wherein

Ar₃ and Ar₄ are identical to the definition of R₁; and

L, Ar, and n are as defined in formula 1;

According to one embodiment of the present disclosure, the compound offormula 2 comprised in the electron transport layer may be representedby the following formula 5 or 6:

wherein

X₁, L₁, Ar₁, and Ar₂ are as defined in formula 1; and

m represents 0 or 1.

In formula 1, X₂ to X₅ each independently represent CR₁ or N.

In formula 1, R₁ represents hydrogen, a substituted or unsubstituted(C1-C30)alkyl, a substituted or unsubstituted (C3-C30)cycloalkyl, asubstituted or unsubstituted (C6-C30)aryl, a substituted orunsubstituted (5- to 30-membered)heteroaryl, a substituted orunsubstituted tri(C1-C30)alkylsilyl, a substituted or unsubstitutedtri(C6-C30)arylsilyl, a substituted or unsubstituteddi(C1-C30)alkyl(C6-C30)arylsilyl, a substituted or unsubstituted(C1-C30)alkyldi(C6-C30)arylsilyl, a substituted or unsubstituted mono-or di-(C1-C30)alkylamino, or a substituted or unsubstituted mono- ordi-(C6-C30)arylamino; or may be linked to an adjacent substituent toform a substituted or unsubstituted, mono- or polycyclic, (C3-C30)alicyclic, aromatic, or a combination of alicyclic and aromatic ring,whose carbon atom(s) may be replaced with at least one heteroatomselected from nitrogen, oxygen, and sulfur. R₁ preferably representshydrogen, a substituted or unsubstituted (C6-C20)aryl, or a substitutedor unsubstituted (5- to 15-membered)heteroaryl; or may be linked to anadjacent substituent to form a substituted or unsubstituted, mono- orpolycyclic, (C6-C15) alicyclic, aromatic, or a combination of alicyclicand aromatic ring; and more preferably represents hydrogen, a(C6-C20)aryl unsubstituted or substituted with a (C1-C6)alkyl or a (5-to 15-membered)heteroaryl, or an unsubstituted (5- to15-membered)heteroaryl; or may be linked to an adjacent substituent toform an unsubstituted, mono- or polycyclic, (C6-C15) alicyclic,aromatic, or a combination of alicyclic and aromatic ring.

In formula 1, L represents a single bond, a substituted or unsubstituted(C6-C50)arylene, or a substituted or unsubstituted (5- to50-membered)heteroarylene. L preferably represents a single bond, asubstituted or unsubstituted (C6-C20)arylene, or a substituted orunsubstituted (5- to 40-membered)heteroarylene, and more preferablyrepresents a single bond, a (C6-C20)arylene unsubstituted or substitutedwith a (C1-C6)alkyl or a (C6-C12)aryl, or a (5- to40-membered)heteroarylene unsubstituted or substituted with a(C1-C6)alkyl or a (C6-C12)aryl.

In formula 1, Ar represents a substituted or unsubstituted (C6-C50)aryl,or a substituted or unsubstituted (5- to 50-membered)heteroaryl. Arpreferably represents a substituted or unsubstituted (C6-C20)aryl, or asubstituted or unsubstituted (5- to 40-membered)heteroaryl, and morepreferably represents a (C6-C20)aryl unsubstituted or substituted with a(C1-C6)alkyl or a (C6-C12)aryl, or a (5- to 40-membered)heteroarylunsubstituted or substituted with a (C1-C6)alkyl or a (C6-C12)aryl.

In formula 2, Ar₁ and Ar₂ each independently represent a substituted orunsubstituted (C6-C30)aryl. Ar₁ and Ar₂ preferably, each independentlyrepresent a substituted or unsubstituted (C6-C20)aryl, and morepreferably, each independently represent an unsubstituted (C6-C20)aryl.

In formula 2, L₁ represents a naphthylene. Specifically, L₁ may berepresented by any one of the following formulae 8 to 10:

wherein

represents a bonding site.

In formula 2, ring A and ring B each independently represent a benzene,a phenylbenzene, or a naphthalene, with a proviso that at least one ofring A and ring B represent naphthalene.

Formula 1 may be represented by formula 11 or 12:

wherein Ar₃, Ar₄, L, and n are as defined in formulae 3 and 4; and

Ar₅ and Ar₆ each independently represent hydrogen, a substituted orunsubstituted (C1-C30)alkyl, a substituted or unsubstituted(C6-C30)aryl, a substituted or unsubstituted (5- to30-membered)heteroaryl, a substituted or unsubstituted(C3-C30)cycloalkyl, a substituted or unsubstituted (C3-C30)cycloalkenyl,a substituted or unsubstituted (3- to 7-membered)heterocycloalkyl, asubstituted or unsubstituted (C1-C30)alkoxy, a substituted orunsubstituted tri(C1-C30)alkylsilyl, a substituted or unsubstitutedtri(C6-C30)arylsilyl, a substituted or unsubstituteddi(C1-C30)alkyl(C6-C30)arylsilyl, a substituted or unsubstituted(C1-C30)alkyldi(C6-C30)arylsilyl, a substituted or unsubstituted mono-or di-(C1-C30)alkylamino, a substituted or unsubstituted mono- ordi-(C6-C30)arylamino, or a substituted or unsubstituted(C1-C30)alkyl(C6-C30)arylamino, or may be linked to an adjacentsubstituent to form a substituted or unsubstituted, mono- or polycyclic,(C3-C30) alicyclic, aromatic, or a combination of alicyclic and aromaticring, whose carbon atom(s) may be replaced with at least one heteroatomselected from nitrogen, oxygen, and sulfur;

the heteroaryl(ene) and the heterocycloalkyl each independently containat least one heteroatom selected from B, N, O, S, Si, and P; and

s and t each independently represent an integer of 1 to 4, and where sor t is an integer of 2 or more, each of Ar₅ or each of Ar₆ may be thesame or different.

The compound represented by formula 1 may be selected from the groupconsisting of the following compounds, but is not limited thereto:

The compound represented by formula 2 may be selected from the groupconsisting of the following compounds, but is not limited thereto:

The compound of formulae 1 and 2 according to the present disclosure canbe prepared by known methods to a person skilled in the art, and can beprepared, for example, by Bromination, Suzuki reaction, Buchwald-Hartwigreaction, Ullmann reaction, etc.

The host compound to be used in the present disclosure may be aphosphorescent host compound or a fluorescent host compound. The kindsof host compound to be used are not particularly limited, and may becompounds having the aforementioned LUMO energy level and selected fromcompounds known in the art. Specifically, the host compound may be afluorescent host compound. The fluorescent host compound may be ananthracene-based compound represented by the following formula 30:

wherein Ar₃₁ and Ar₃₂, each independently, represent a substituted orunsubstituted (C6-C30)aryl, or a substituted or unsubstituted (5- to30-membered) heteroaryl; Ar₃₃ and Ar₃₄, each independently, representhydrogen, deuterium, a halogen, a cyano, a nitro, a hydroxy, asubstituted or unsubstituted (C1-C30)alkyl, a substituted orunsubstituted (C6-C30)aryl, a substituted or unsubstituted (5- to30-membered) heteroaryl, a substituted or unsubstituted(C3-C30)cycloalkyl, a substituted or unsubstituted (C1-C30)alkoxy, asubstituted or unsubstituted (C1-C30)alkylsilyl, a substituted orunsubstituted (C6-C30)arylsilyl, a substituted or unsubstituted(C6-C30)aryl(C1-C30)alkylsilyl, or —NR₄₁R₄₂; R₄₁ and R₄₂, eachindependently, represent hydrogen, a substituted or unsubstituted(C6-C30)aryl, or a substituted or unsubstituted (5- to 30-membered)heteroaryl, or may be bonded to each other to form a mono- orpolycyclic, (C3-C30) alicyclic, aromatic, or a combination of alicyclicand aromatic ring whose carbon atom(s) may be replaced with at least oneheteroatom selected from nitrogen, oxygen, and sulfur; gg and hh, eachindependently, represent an integer of 1 to 4; and where gg or hh is aninteger of 2 or more, each of Ar₃₃ or Ar₃₄ may be the same or different.

Specifically, the compound of formula 30 includes the followingcompounds, but is not limited thereto:

The dopant compound to be used in the present disclosure may be aphosphorescent dopant compound or a fluorescent dopant compound.Specifically, the dopant compound may be a fluorescent dopant compound.The fluorescent dopant compound may be a condensed polycyclic aminederivative represented by the following formula 40:

wherein Ar₄₁ represents a substituted or unsubstituted (C6-C50)aryl orstyryl; L_(a) represents a single bond, a substituted or unsubstituted(C6-C30)arylene, or a substituted or unsubstituted (3- to30-membered)heteroarylene; Ar₄₂ and Ar₄₃, each independently, representhydrogen, deuterium, a halogen, a substituted or unsubstituted(C1-C30)alkyl, a substituted or unsubstituted (C6-C30)aryl, or asubstituted or unsubstituted (3- to 30-membered)heteroaryl, or may belinked to an adjacent substituent(s) to form a mono- or polycyclic,(C3-C30) alicyclic, aromatic, or a combination of alicyclic and aromaticring whose carbon atom(s) may be replaced with at least one heteroatomselected from nitrogen, oxygen, and sulfur; jj represents 1 or 2; andwhere jj is 2, each of

may be the same or different.

A preferable aryl for Ar₄₁ includes a substituted or unsubstitutedphenyl, a substituted or unsubstituted fluorenyl, a substituted orunsubstituted anthryl, a substituted or unsubstituted pyrenyl, asubstituted or unsubstituted chrysenyl, a substituted or unsubstitutedbenzofluorenyl, and spiro[fluoren-benzofluorene], etc.

Specifically, the compound of formula 40 includes the followingcompounds, but is not limited thereto:

The organic electroluminescent device of the present disclosure mayfurther comprise a hole injection layer or a hole transport layerbetween the first electrode and the light-emitting layer.

Hereinafter, referring to FIG. 1, the structure of an organicelectroluminescent device, and a method for preparing it will bedescribed in detail.

FIG. 1 illustrates a schematic sectional view of an organicelectroluminescent device according to one embodiment of the presentdisclosure.

FIG. 1 shows an organic electroluminescent device 100 comprising asubstrate 101, a first electrode 110 formed on the substrate 101, anorganic layer 120 formed on the first electrode 110, and a secondelectrode 130 formed on the organic layer 120 and facing the firstelectrode 110.

The organic layer 120 comprises a hole injection layer 122, a holetransport layer 123 formed on the hole injection layer 122, alight-emitting layer 125 formed on the hole transport layer 123, anelectron buffer layer 126 formed on the light-emitting layer 125, and anelectron transport zone 129 formed on the electron buffer layer 126; andthe electron transport zone 129 comprises an electron transport layer127 formed on the electron buffer layer 126, and an electron injectionlayer 128 formed on the electron transport layer 127.

The light-emitting layer 125 may be prepared with a host compound and adopant compound. The kinds of host compound and dopant compound to beused are not particularly limited, and may be selected from compoundsknown in the art. The examples of the host compound and the dopantcompound are as described above. When the light-emitting layer 125comprises a host and a dopant, the dopant can be doped in an amount ofless than about 25 wt %, and preferably less than 17 wt %, based on thetotal amount of the dopant and host of the light-emitting layer. Whenthe light emitting layer 125 is composed of two or more layers, each ofthe layers may be prepared to emit color different from one another. Forexample, the device may emit white light by preparing threelight-emitting layers 125 which emit blue, red, and green colors,respectively. Furthermore, the device may include light-emitting layerswhich emit yellow or orange color, if necessary.

The electron buffer layer 126 may employ the compound of formula 1 ofthe present disclosure or other compounds for the electron buffer. Thethickness of the electron buffer layer 126 is 1 nm or more, but is notparticularly limited thereto. Specifically, the thickness of theelectron buffer layer 126 may be in the range of from 2 nm to 200 nm.The electron buffer layer 126 may be formed on the light-emitting layer125 by using known various methods such as vacuum deposition, wetfilm-forming methods, laser induced thermal imaging, etc. The electronbuffer layer indicates a layer controlling an electron flow. Therefore,the electron buffer layer may be, for example, a layer which trapselectrons, blocks electrons, or lowers an energy barrier between anelectron transport zone and a light-emitting layer.

The electron transport zone 129 means a zone in which electrons aretransported from the second electrode to the light-emitting layer. Theelectron transport zone 129 can comprise an electron transport compound,a reductive dopant, or a combination thereof. The electron transportcompound can be at least one selected from a group comprisingtriazine-based compounds, oxazole-based compounds, isoxazole-basedcompounds, triazole-based compounds, isothiazole-based compounds,oxadiazole-based compounds, thiadiazole-based compounds, perylene-basedcompounds, anthracene-based compounds, aluminum complexes, and galliumcomplexes. The reductive dopant may be selected from alkali metals,alkali metal compounds, alkaline earth metals, rare-earth metals, andhalides, oxides, and complexes thereof. Specifically, the reductivedopant includes lithium quinolate, sodium quinolate, cesium quinolate,potassium quinolate, LiF, NaCl, CsF, Li₂O, BaO, and BaF₂, but are notlimited thereto. In addition, the electron transport zone 129 cancomprise an electron transport layer 127, an electron injection layer128, or both of them. The electron transport layer 127 and the electroninjection layer 128 can each be composed of two or more layers. Theelectron transport layer 127 can comprise an electron transport materialincluding the compound represented by formula 2. In addition, theelectron transport layer 127 can further comprise the reductive dopantabove.

The electron injection layer 128 may be prepared with any electroninjection material known in the art, which includes lithium quinolate,sodium quinolate, cesium quinolate, potassium quinolate, LiF, NaCl, CsF,Li₂O, BaO, and BaF₂, but is not limited thereto.

The aforementioned description regarding the organic electroluminescentdevice shown in FIG. 1 is intended to explain one embodiment of theinvention, and is not meant in any way to restrict the scope of theinvention. The organic electroluminescent device can be constructed inanother way. For example, any one optional component such as a holeinjection layer may not be comprised in the organic electroluminescentdevice of FIG. 1, except for a light-emitting layer and an electronbuffer layer. In addition, an optional component may be furthercomprised therein, which includes one or more of an impurity layer suchas n-doping layer and p-doping layer. The organic electroluminescentdevice may be a both side emission type in which a light-emitting layeris placed on each of both sides of the impurity layer. The twolight-emitting layers on the impurity layer may emit different colors.The organic electroluminescent device may be a bottom emission type inwhich a first electrode is a transparent electrode and a secondelectrode is a reflective electrode. The organic electroluminescentdevice may be a top emission type in which a first electrode is areflective electrode and a second electrode is a transparent electrode.The organic electroluminescent device may have an inverted typestructure in which a cathode, an electron transport layer, alight-emitting layer, a hole transport layer, a hole injection layer,and an anode are sequentially stacked on a substrate.

FIG. 2 illustrates an energy gap relationship among the layers of theorganic electroluminescent device according to one embodiment of thepresent disclosure.

In FIG. 2, a hole transport layer 123, a light-emitting layer 125, anelectron buffer layer 126, and an electron transport zone 129 aresequentially stacked. Electrons (e⁻) injected from a cathode aretransported to a light-emitting layer 125 through an electron transportzone 129 and an electron buffering layer 126.

The LUMO energy level of the electron buffer layer 126 has a mediumvalue of the LUMO energy level of the host compound and the dopantcompound of the light-emitting layer 125 and the LUMO energy level ofthe electron transport layer 127. Specifically, the LUMO energy levelsof the layers have a relationship of the electron transportlayer>electron buffer layer>light-emitting layer. As in FIG. 2, a LUMOenergy gap of 0.5 eV or greater occurs between the light-emitting layerand the electron transport layer. However, by inserting an electronbuffer layer, there is an advantage in that electrons can be activelytransported.

According to one embodiment of the organic electroluminescent device ofthe present disclosure, the LUMO energy level of the light-emittinglayer (Ah) is higher than the LUMO energy level of the dopant compound(Ad).

According to one embodiment of the organic electroluminescent device ofthe present disclosure, the LUMO energy level of the electron transportlayer (Ae) is higher than the LUMO energy level of the electron bufferlayer (Ab).

According to one embodiment of the organic electroluminescent device ofthe present disclosure, the LUMO energy level of the electron transportlayer (Ae) and the LUMO energy level of the light-emitting layer (Ah)satisfy the following equation.Ae≤Ah+0.5 eV

For appropriate efficiency and long lifespan, the LUMO energy level ofthe electron transport layer (Ae) and the LUMO energy level of theelectron buffer layer (Ab) satisfy the following equation.Ae≤Ab+0.2˜0.3 eV

The results according to the relationship of the LUMO energy levels ofthe electron transport layer (Ae), electron buffer layer (Ab), and thelight-emitting layer (Ah) are for explaining the rough tendency of thedevice in accordance with the overall LUMO energy groups, and so resultsother than the above can appear according to the inherent property ofthe specific derivatives, and the stability of the materials.

The electron buffer layer can be comprised in organic electroluminescentdevices emitting every color including blue, red, and green. Preferably,it can be comprised in an organic electroluminescent device emittingblue light (i.e. the main peak wavelength is from 430 to 470 nm,preferably, in the 450's nm).

By using the organic electroluminescent device of the presentdisclosure, a display system, for example, for smartphones, tablets,notebooks, PCs, TVs, or vehicles, or a lighting system, for example, anindoor or outdoor lighting system, can be produced.

Hereinafter, the luminous properties of the organic electroluminescentdevice of the present disclosure will be explained in detail.

Comparative Example 1: Producing a Blue Light-Emitting OLED Device notAccording to the Present Disclosure

An OLED device not according to the present disclosure was produced asfollows: A transparent electrode indium tin oxide (ITO) thin film (10Ω/sq) on a glass substrate for an OLED (GEOMATEC CO., LTD., Japan) wassubjected to an ultrasonic washing with acetone and isopropyl alcohol,sequentially, and then was stored in isopropanol. Next, the ITOsubstrate was mounted on a substrate holder of a vacuum vapor depositionapparatus.N⁴,N^(4′)-diphenyl-N⁴,N^(4′)-bis(9-phenyl-9H-carbazol-3-yl)-[1,1′-biphenyl]-4,4′-diamine(Compound HI-1) was introduced into a cell of the vacuum vapordeposition apparatus, and the pressure in the chamber of the apparatuswas then controlled to 10⁻⁷ torr. Thereafter, an electric current wasapplied to the cell to evaporate the introduced material, therebyforming a first hole injection layer having a thickness of 60 nm on theITO substrate. 1,4,5,8,9,12-hexaazatriphenylene-hexacarbonitrile(Compound HI-2) was then introduced into another cell of the vacuumvapor deposition apparatus, and an electric current was applied to thecell to evaporate the introduced material, thereby forming a second holeinjection layer having a thickness of 5 nm on the first hole injectionlayer.N-([1,1′-biphenyl]-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluorene-2-amine(Compound HT-1) was introduced into another cell of the vacuum vapordeposition apparatus. Thereafter, an electric current was applied to thecell to evaporate the introduced material, thereby forming a first holetransport layer having a thickness of 20 nm on the second hole injectionlayer.9-(naphthalen-2-yl)-3-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-carbazole(Compound HT-2) was then introduced into another cell of the vacuumvapor deposition apparatus, and an electric current was applied to thecell to evaporate the introduced material, thereby forming a second holetransport layer having a thickness of 5 nm on the first hole transportlayer. After forming the hole injection layers and the hole transportlayers, a light-emitting layer was then deposited as follows. CompoundH-82 as a host was introduced into one cell of the vacuum vapordeposition apparatus and compound D-38 as a dopant was introduced intoanother cell of the apparatus. The two materials were evaporated at adifferent rate and the dopant was deposited in a doping amount of 2 wt%, based on the total weight of the host and dopant, to form alight-emitting layer having a thickness of 20 nm on the second holetransport layer. Next, BCP (compound ETL-1) as an electron transportmaterial was introduced into one cell of the vacuum vapor depositionapparatus and evaporated to form an electron transport layer having athickness of 35 nm on the light-emitting layer. After depositing lithiumquinolate (compound EIL-1) as an electron injection layer having athickness of 2 nm on the electron transport layer, an Al cathode havinga thickness of 80 nm was deposited by another vacuum vapor depositionapparatus on the electron injection layer. Thus, an OLED device wasproduced. All the materials used for producing the OLED device werepurified by vacuum sublimation at 10⁻⁶ torr.

The driving voltage, luminous efficiency, CIE color coordinates, and thetime period for the luminance to decrease from 100% to 90% at aluminance of 1,000 nits of the produced OLED device are provided inTable 1 below. In addition, a current efficiency versus a luminance ofthe organic electroluminescent device of Comparative Example 1 isillustrated in FIG. 3 as a graph.

Comparative Example 2: Producing a Blue Light-Emitting OLED Device notAccording to the Present Disclosure

An OLED device was produced in the same manner as in Comparative Example1, except that Alq₃ (compound ETL-2) was used as an electron transportmaterial, and evaluated. The evaluation results of the OLED device ofComparative Example 2 are provided in Table 1 below.

Comparative Examples 3 and 4: Producing a Blue Light-Emitting OLEDDevice not According to the Present Disclosure

OLED devices were produced in the same manner as in Comparative Example1, except that BCP (compound ETL-1) was evaporated as an electron bufferlayer of 5 nm and Alq₃ (compound ETL-2) was evaporated as an electrontransport layer of 30 nm (Comparative Example 3), and compound B-21 wasevaporated as an electron buffer layer of 5 nm and compound ETL-3 andLiq in a weight ratio of 50:50 were evaporated as an electron transportlayer of 30 nm (Comparative Example 4) instead of forming an electrontransport layer of 35 nm, and evaluated. The evaluation results of theOLED device of Comparative Examples 3 and 4 are provided in Table 1below.

Comparative Examples 5 to 8: Producing a Blue Light-Emitting OLED Devicenot According to the Present Disclosure

OLED devices were produced in the same manner as in Comparative Example1, except that an electron buffer layer is not formed and the compoundsof Table 1 and Liq in a weight ratio of 50:50 were evaporated as anelectron transport layer of 30 nm, and evaluated. The evaluation resultsof the OLED device of Comparative Examples 5 to 8 are provided in Table1 below.

Device Examples 1 to 4: Producing a Blue Light-Emitting OLED DeviceAccording to the Present Disclosure

In Device Examples 1 to 4, OLED devices were produced in the same manneras in Comparative Example 1, except that compound B-21 was evaporated asan electron buffer layer of 5 nm and the compounds of Table 1 and Liq ina weight ratio of 50:50 were evaporated as an electron transport layerof 30 nm, and evaluated. The evaluation results of the OLED device ofDevice Examples 1 to 4 are provided in Table 1 below. In addition, acurrent efficiency versus a luminance of the organic electroluminescentdevice of Device Example 2 is illustrated in FIG. 3 as a graph.

TABLE 1 Electron Electron Driving Luminous Color Color Buffer TransportVoltage Efficiency Coordinate Coordinate Lifespan Layer Layer (V) (cd/A)(x) (y) (T90, hr) Comparative — ETL-1 5.8 5.0 0.140 0.095 0.15 Example 1Comparative — ETL-2 4.6 4.3 0.144 0.105 4.04 Example 2 Comparative ETL-1ETL-2 5.2 4.2 0.141 0.097 0.7 Example 3 Comparative B-21 ETL-3:Liq 3.96.0 0.140 0.099 43.8 Example 4 Comparative — C-1:Liq 4.5 3.8 0.141 0.09654.6 Example 5 Comparative — C-2:Liq 5.1 3.3 0.139 0.098 55.6 Example 6Comparative — C-3:Liq 5.0 3.8 0.139 0.095 51.5 Example 7 Comparative —C-4:Liq 4.9 3.0 0.139 0.096 50.1 Example 8 Device B-21 C-1:Liq 4.1 5.50.140 0.095 56.5 Example 1 Device B-21 C-2:Liq 4.3 5.8 0.139 0.099 63.9Example 2 Device B-21 C-3:Liq 4.4 5.7 0.139 0.097 58.9 Example 3 DeviceB-21 C-4:Liq 4.0 5.8 0.139 0.097 58.1 Example 4

Comparative Examples 9 and 10: Producing a Blue Light-Emitting OLEDDevice not According to the Present Disclosure

OLED devices were produced in the same manner as in Comparative Example1, except for using compound H-15 as the host compound and using theelectron transport material as in Table 2, and evaluated. The evaluationresults of the OLED device of Comparative Examples 9 and 10 are providedin Table 2 below.

Comparative Example 11: Producing a Blue Light-Emitting OLED Device notAccording to the Present Disclosure

An OLED device was produced in the same manner as in ComparativeExamples 9 and 10, except that BCP (compound ETL-1) was evaporated as anelectron buffer layer of 5 nm and Alq₃ (compound ETL-2) was evaporatedas an electron transport layer of 30 nm instead of forming an electrontransport layer of 35 nm, and evaluated. The evaluation results of theOLED device of Comparative Example 11 are provided in Table 2 below.

Comparative Examples 12 to 14: Producing a Blue Light-Emitting OLEDDevice not According to the Present Disclosure

OLED devices were produced in the same manner as in Comparative Examples9 and 10, except that an electron buffer layer is not formed and thecompounds of Table 2 and Liq in a weight ratio of 50:50 were evaporatedas an electron transport layer of 30 nm, and evaluated. The evaluationresults of the OLED device of Comparative Examples 12 to 14 are providedin Table 2 below.

Device Examples 5 to 7: Producing a Blue Light-Emitting OLED DeviceAccording to the Present Disclosure

In Device Examples 5 to 7, OLED devices were produced in the same manneras in Comparative Examples 9 and 10, except that compound B-28 wasevaporated as an electron buffer layer of 5 nm and the compounds ofTable 2 and Liq in a weight ratio of 50:50 were evaporated as anelectron transport layer of 30 nm, and evaluated. The evaluation resultsof the OLED device of Device Examples 5 to 7 are provided in Table 2below.

TABLE 2 Electron Electron Driving Luminous Color Color Buffer TransportVoltage Efficiency Coordinate Coordinate Lifespan Layer Layer (V) (cd/A)(x) (y) (T90, hr) Comparative ETL-1 6.4 4.7 0.140 0.089 0.13 Example 9Comparative ETL-2 5.2 4.0 0.146 0.105 1.9 Example 10 Comparative ETL-1ETL-2 5.8 4.0 0.141 0.091 0.56 Example 11 Comparative C-7:Liq 5.2 2.90.141 0.093 36.1 Example 12 Comparative C-1:Liq 5.3 3.3 0.140 0.091 41.0Example 13 Comparative C-43:Liq 5.9 2.8 0.140 0.089 37.9 Example 14Device B-28 C-7:Liq 4.3 6.0 0.139 0.088 71.4 Example 5 Device C-1:Liq4.5 5.9 0.139 0.088 72.8 Example 6 Device C-43:Liq 5.0 5.5 0.139 0.08886.8 Example 7

From Tables 1 and 2 above, it can be seen that the OLED devices ofDevice Examples 1 to 4 and Device Examples 5 and 7 provide lower drivingvoltage, higher efficiency, and longer lifespan compared to ComparativeExamples 1 to 4 and Comparative Examples 9 to 11, respectively, byappropriately combining the electron buffer layer and the electrontransport layer of the present disclosure. In addition, upon comparingComparative Examples 5 to 8 and Comparative Examples 12 to 14 withDevice Examples 1 to 4 and Device Examples 5 and 7, respectively, it canbe seen that the driving voltage, efficiency, and lifespancharacteristics are all improved according to the insertion of theelectron buffer layer between the light-emitting layer and the electrontransport layer. This means that the electron injection characteristiccan be improved according to the combination of the electron bufferlayer and the electron transport layer, which may be due to an activecascade of the LUMO energy level. For one example, the LUMO energy levelof the light-emitting layer may be 1.6 eV, and when a 1,4-naphthyl groupis comprised as a linker between a carbazole derivative and a triazine,the LUMO energy level may be 2.1 eV. In this case, the energy barrierbetween the light-emitting layer and the electron transport layer is ashigh as about 0.5 eV so that a high driving voltage and low efficiencycharacteristics can be shown as in Comparative Examples 5 to 8. However,if an electron buffer layer of the compound of the present disclosure isinserted between the light-emitting layer and the electron transportlayer, the electron injection barrier is improved as in FIG. 2 so thatthe driving voltage, efficiency, and lifespan characteristics are allimproved. This is the case only when the linker of the electrontransport material is one aryl. The reason is that in the case of acompound having a linker comprising two or more aryl groups, theconjugation length becomes longer, which results in low LUMO energylevel. This leads to a big difference between the LUMO energy level ofthe light-emitting layer and the electron transport layer, and aninappropriateness as a use for an electron transport layer.

Due to lifespan increase, the combination of the electron buffer layerand the electron transport layer is considered to be easily applied toflexible displays, lightings, and vehicle displays which require longlifespan.

TABLE 3 Compounds used in Comparative Examples and Device Examples HoleInjection Layer/ Hole Transport Layer

HI-1

HI-2

HT-1

HT-2 Light-Emitting Layer

H-82

H-15

D-38 Electron Buffer Layer/ Electron Transport Layer/ Electron InjectionLayer

B-21

B-28

ETL-1

ETL-2

ETL-3

C-1

C-2

C-3

C-4

C-7

C-43

EIL-1

REFERENCE NUMBERS

  100: organic electroluminescent device 101: substrate 110: firstelectrode 120: organic layer 122: hole injection layer 123: holetransport layer 125: light-emitting layer 126: electron buffer layer127: electron transport layer 128: electron injection layer 129:electron transport zone 130: second electrode

What is claimed is:
 1. An organic electroluminescent device comprising afirst electrode, a second electrode facing the first electrode, alight-emitting layer between the first electrode and the secondelectrode, and an electron transport layer and an electron buffer layerbetween the light-emitting layer and the second electrode, wherein theelectron buffer layer comprises a compound represented by the followingformula 1, and the electron transport layer comprises a compoundrepresented by the following formula 2:

wherein X₁ to X₅ each independently represent CR₁ or N; R₁ representshydrogen, a substituted or unsubstituted (C1-C30)alkyl, a substituted orunsubstituted (C3-C30)cycloalkyl, a substituted or unsubstituted(C6-C30)aryl, a substituted or unsubstituted (5- to30-membered)heteroaryl, a substituted or unsubstitutedtri(C1-C30)alkylsilyl, a substituted or unsubstitutedtri(C6-C30)arylsilyl, a substituted or unsubstituteddi(C1-C30)alkyl(C6-C30)arylsilyl, a substituted or unsubstituted(C1-C30)alkyldi(C6-C30)arylsilyl, a substituted or unsubstituted mono-or di-(C1-C30)alkylamino, or a substituted or unsubstituted mono- ordi-(C6-C30)arylamino; or may be linked to an adjacent substituent toform a substituted or unsubstituted, mono- or polycyclic, (C3-C30)alicyclic, aromatic, or a combination of alicyclic and aromatic ring,whose carbon atom(s) may be replaced with at least one heteroatomselected from nitrogen, oxygen, and sulfur; L represents a single bond,a substituted or unsubstituted (C6-C50)arylene, or a substituted orunsubstituted (5- to 50-membered)heteroarylene; Ar represents asubstituted or unsubstituted (C6-C50)aryl, or a substituted orunsubstituted (5- to 50-membered)heteroaryl; Ar₁ and Ar₂ eachindependently represent a substituted or unsubstituted (C6-C30)aryl; L₁represents a naphthylene; ring A and ring B each independently representa benzene, a phenylbenzene, or a naphthalene, with a proviso that atleast one of ring A and ring B represent naphthalene; n represents aninteger of 1 to 3; and the heteroaryl(ene) contains at least oneheteroatom selected from B, N, O, S, Si, and P.
 2. The organicelectroluminescent device according to claim 1, wherein formula 1 isrepresented by the following formula 3 or 4:

wherein Ar₃ and Ar₄ are identical to the definition of R₁; and L, Ar,and n are as defined in claim
 1. 3. The organic electroluminescentdevice according to claim 1, wherein formula 2 is represented by thefollowing formula 5 or 6:

wherein X₁, L₁, Ar₁, and Ar₂ are as defined in claim 1; and m represents0 or
 1. 4. The organic electroluminescent device according to claim 1,wherein in formula 2, L₁ is represented by any one of the followingformulae 8 to 10:

wherein

represents a bonding site.
 5. The organic electroluminescent deviceaccording to claim 1, wherein the compound represented by formula 1 isselected from the group consisting of:


6. The organic electroluminescent device according to claim 1, whereinthe compound represented by formula 2 is selected from the groupconsisting of:


7. The organic electroluminescent device according to claim 1, whereinthe light-emitting layer comprises a host compound and a dopantcompound, the LUMO (lowest unoccupied molecular orbital) energy level ofthe electron buffer layer is higher than the LUMO energy level of thehost compound, and the LUMO energy level of the electron transport layeris higher than the LUMO energy level of the electron buffer layer. 8.The organic electroluminescent device according to claim 1, wherein theLUMO energy level of the electron transport layer (Ae) and the LUMOenergy level of the light-emitting layer (Ah) satisfy the followingequation:Ae≤Ah+0.5 eV.
 9. The organic electroluminescent device according toclaim 1, wherein the LUMO energy level of the electron transport layer(Ae) and the LUMO energy level of the electron buffer layer (Ab) satisfythe following equation:Ae≤Ab+0.2˜0.3 eV.
 10. The organic electroluminescent device according toclaim 1, wherein the electron transport layer further comprises areductive dopant.